Format

Send to

Choose Destination
J Pharmacol Exp Ther. 2018 Jul;366(1):75-83. doi: 10.1124/jpet.118.247734. Epub 2018 Apr 23.

The Extracellular cAMP-Adenosine Pathway in Airway Smooth Muscle.

Author information

1
Division of Cellular Pharmacology, Department of Pharmacology, Escola Paulista de Medicina, Universidade Federal de São Paulo (EPM/UNIFESP), São Paulo, Brazil.
2
Division of Cellular Pharmacology, Department of Pharmacology, Escola Paulista de Medicina, Universidade Federal de São Paulo (EPM/UNIFESP), São Paulo, Brazil godinho@unifesp.br.

Abstract

In the respiratory tract, intracellular cAMP has a key role in the smooth muscle relaxation induced by the β2-adrenoceptor/Gs protein/adenylyl cyclase axis. In other tissues, cAMP also works as an extracellular messenger, after its efflux and interstitial conversion to adenosine by ectoenzymes. The aim of this study was to identify cAMP efflux and the "extracellular cAMP-adenosine pathway" in the airway smooth muscle. First, we tested the ability of β2-adrenoceptor agonists formoterol or fenoterol to increase the extracellular cAMP in isolated tracheal rings from adult male Wistar rats. The effects of adenosine, cAMP, 8-Br-cAMP, fenoterol, or formoterol were also evaluated in the isometric contraction of control or carbachol (CCh) precontracted tracheas, normalized as the percentage of CCh-induced response. Fenoterol and formoterol induced 70%-80% relaxation and increased extracellular cAMP levels by up to 280%-450%. Although exogenous cAMP or adenosine evoked phasic contractions, the membrane-permeable cAMP analog 8-Br-cAMP induced relaxation of CCh-precontracted tracheas. The simultaneous inhibition of adenosine degradation/uptake with EHNA [erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride] plus uridine increased by 3-fold the maximum cAMP-induced contraction, whereas it was significantly reduced by AMPCP [adenosine 5'-(α,β-methylene)diphosphate; an ecto-5'-nucleotidase inhibitor], and by adenosine receptor antagonists CGS-15943 (nonselective) or DPCPX (8-cyclopentyl-1,3-dipropylxanthine) (A1 selective). Finally, CGS-15943 shifted to the left the concentration-relaxation curve for fenoterol. In conclusion, our results show that airway smooth muscle expresses the extracellular cAMP-adenosine pathway associated with contracting effects mediated by A1 receptors. The cAMP efflux triggered by fenoterol/formoterol indicates that the extracellular cAMP-adenosine pathway may play a role in balancing the relaxant effects of β2-adrenoceptor agonists in airways, which may impact their bronchodilation effects.

PMID:
29685885
DOI:
10.1124/jpet.118.247734

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center